Photoshop Layers Problem

I need to add layers to an existing image so that I can modify them as I was directed. The problem, however, is that on the Layers palette of Photoshop 6, the option for adding layers to the image is grayed out and inaccessible. Additionally, the symbol of a lock is displayed to the right of the existing layer the image is on. Clicking or right-clicking the lock doesn’t help.

Therefore, my question is, how do I get rid of the lock icon so that I can add layers to the image? Re-saving the original BMP image file in native PSD file format doesn’t help.